1. Field of the Invention
The present invention relates to a dispersion-compensating fiber, a dispersion compensator, and an optical transmission line that has a signal-transmitting fiber and a dispersion-compensating fiber.
2. Description of the Background Art
An optical transmission line for transmitting a signal lightwave in an optical transmission system is required to have a small insertion loss and a small absolute value of overall dispersion in the wavelength band for the signal lightwave so that a large volume of information can be transmitted. It is difficult to reduce the absolute value of overall dispersion of an optical transmission line by using only a single type of optical fiber. Consequently, the absolute value of overall dispersion is reduced by connecting a plurality of types of optical fibers (see U.S. Pat. No. 6,574,407, for example).
More specifically, to reduce the absolute value of overall dispersion of an optical transmission line in the wavelength band for the signal lightwave, the following two types of optical fibers are connected in series with a proper ratio in length: one is a signal-transmitting fiber having a positive chromatic dispersion in the wavelength band for the signal lightwave and the other is a dispersion-compensating fiber having a negative chromatic dispersion in the wavelength band for the signal lightwave. In this case, when the signal-transmitting fiber and the dispersion-compensating fiber have a dispersion slope different in sign from each other, the absolute value of overall dispersion of the optical transmission line can be reduced in a broad wavelength band.
However, conventional dispersion-compensating fibers, including the optical transmission line disclosed in the foregoing U.S. Pat. No. 6,574,407, cannot sufficiently reduce both the insertion loss and the absolute value of overall dispersion of an optical transmission line in a broad wavelength band. Therefore, they are not adequate to be used for large-capacity optical transmission.